Embodiments of the present invention relate to a semiconductor device, and more particularly to a semiconductor device and a method for forming the same.
The electronic industry has recently been intensively focused on the development of a method for manufacturing a highly-integrated semiconductor device. In order to implement a highly-integrated semiconductor device, fabrication technology for a semiconductor substrate has been rapidly changing to improve technology for fabricating a more-miniaturized semiconductor substrate. Therefore, a semiconductor device design rule, serving as an indicator as to how many separate elements can be formed on a limited-sized semiconductor substrate, has become more strict. In accordance with the design rule, the more a pattern minimizes, the narrower the distance between respective patterns becomes and the more precise pattern shape must be.
As a semiconductor device becomes super miniaturized and highly integrated, the design rule of the semiconductor device is gradually reduced, so that a channel length of a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) becomes shorter. The reduced channel length causes the distance between a source region and a drain region to be reduced, thereby causing a short channel effect (SCE). As a result, it is difficult to effectively control the influence of a drain-region voltage on a source-region voltage and a channel-region voltage, and thus characteristics of an active switch are unavoidably deteriorated. In addition, when the distance between the source region and the drain region is very close, the punch-through influence between the source and drain.
In order to solve the above-mentioned problems, a Recessed Field Effect Transistor (FET) structure, in which a semiconductor substrate is recessed and a gate electrode is formed to bury the recessed semiconductor substrate so that an effective channel length is increased, has been proposed. The recessed FET structure improves the source and drain punch-through phenomena by substantially increasing the distance between the source and drain regions.
However, the recess gate is disadvantageous in that it is difficult to control a threshold voltage (Vt). Thus the threshold voltage (Vt) is reduced and a leakage current occurs in an OFF state. In order to control the threshold voltage (Vt), impurity ions such as boron (B) need to be implanted. However, such additional impurity ion implantation causes the electric field of a device to increase, and thus device refresh characteristics are deteriorated.
In addition, the semiconductor substrate is deeply etched to form a recess gate, which deteriorates gate control function due to an increased body effect and results in deterioration of swing characteristics. Furthermore, device characteristics deteriorate because of a neighbor gate effect between neighboring recess gates.